Project Summary: Compared to neurosensory hyperacusis, many more patients suffer from conductive hyperacusis due to mechanical abnormalities of the ear that result in hypersensitivity to sound/vibration transmitted through their bodies. The symptoms of conductive hyperacusis are characterized by an increased and even distorted sensation of self- generated or certain external sounds, including one's own voice (autophony), pulsatile blood flow, footsteps, joint movements, eye movements, and machinery vibrations as from vehicles. These symptoms are common among patients who suffer pathological third-window lesions such as superior canal dehiscence, where an opening occurs in the bone encapsulating the inner ear. Conductive hyperacusis, due to abnormalities in the passive mechanical system, may be treatable. Recent surgical treatments for hyperacusis that change the mechanics of structures surrounding the inner ear show mixed results with some patients experiencing worse symptoms after surgery. Although these ?experimental? surgical treatments in patients are increasing, the mechanisms of conductive hyperacusis are not well understood, and scientific research targeting this problem is lacking. The goal of the proposed research plan is to understand how mechanical changes in fresh cadaveric ears, with similar mechanics to the living ear, can increase the cochlear drive (an estimate of hearing) as in hyperacusis. Our novel intracochlear pressure measurement technique will monitor the cochlear drive as we manipulate the mechanics in the middle and inner ear. We aim to: 1) measure effects of superior canal dehiscence and near-dehiscence on cochlear drive during bone conduction stimulation; 2) determine the contribution of middle-ear ossicles to hyperacusis; and 3) elucidate mechanisms of conductive hyperacusis using a finite-element model. This study will increase our understanding of hyperacusis resulting from mechanical pathologies. Such knowledge will provide the scientific foundation necessary for the development of effective treatment plans for a disease that is debilitating for millions of people.